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LTC3210-3 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3210-3 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  LTC3210-2/LTC3210-3 10 321023fa OPERATION Figure 2. Charge Pump Thevenin Equivalent Open-Loop Circuit + – ROL CPO 1.5VBAT OR 2VBAT + – 321023 F02 Soft-Start Initially, when the part is in shutdown, a weak switch con- nects VBAT to CPO. This allows VBAT to slowly charge the CPO output capacitor to prevent large charging currents. The LTC3210-2/LTC3210-3 also employ a soft-start feature on its charge pump to prevent excessive inrush current and supply droop when switching into the step-up modes. The current available to the CPO pin is increased linearly over a typical period of 150μs. Soft-start occurs at the start of both 1.5x and 2x mode changes. Charge Pump Strength and Regulation Regulation is achieved by sensing the voltage at the CPO pin and modulating the charge pump strength based on the error signal. The CPO regulation voltages are set internally, and are dependent on the charge pump modes as shown in Table 1. Table 1. Charge Pump Output Regulation Voltages Charge Pump Mode Regulated VCPO 1.5x 4.55V 2x 5.05V When the LTC3210-2/LTC3210-3 operate in either 1.5x mode or 2x mode, the charge pump can be modeled as a Thevenin-equivalent circuit to determine the amount of current available from the effective input voltage and ef- fective open-loop output resistance, ROL (Figure 2). ROL is dependent on a number of factors including the switching term, 1/(2fOSC • CFLY), internal switch resis- tances and the nonoverlap period of the switching circuit. However, for a given ROL, the amount of current available will be directly proportional to the advantage voltage of 1.5VBAT – CPO for 1.5x mode and 2VBAT – CPO for 2x mode. Consider the example of driving white LEDs from a 3.1V supply. If the LED forward voltage is 3.8V and the current sources require 100mV, the advantage voltage for 1.5x mode is 3.1V • 1.5 – 3.8V – 0.1V or 750mV. Notice that if the input voltage is raised to 3.2V, the advantage voltage jumps to 900mV—a 20% improvement in avail- able strength. |
Similar Part No. - LTC3210-3 |
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Similar Description - LTC3210-3 |
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